1. Field of the Invention
The present invention relates to a capacitor, a method of manufacture thereof, and a semiconductor device which incorporates the capacitor.
Priority is claimed on Japanese Patent Applications Nos. 2003-303173 and 2003-303174, both filed Aug. 27, 2003, the contents of which are incorporated herein by reference.
2. Description of Related Art
Various types of capacitors are utilized as constructional elements in semiconductor devices, as for example disclosed in Japanese Unexamined Patent Applications, First Publications Nos. H07-226485, H09-139480, H05-82801, and H05-47587. For example, in oscillator circuits or power supply circuits which are implemented as semiconductor devices, capacitors are utilized for an operational amplifier (op-amp) oscillation prevention, stabilization, and smoothing, and in booster circuits and the like.
As such a capacitor, if it is to be fitted internally to a circuit which is being constructed, a structure is often utilized in which a dielectric layer such as a silicon oxide layer, a silicon nitride layer, or an oxidized silicon nitride layer or the like is sandwiched between upper and lower electrode layers which are made from silicon, metal, or titanium nitride, aluminum nitride, or the like. Furthermore, as a type of capacitor which is utilized for being fitted externally to a circuit or the like, there is a type which consists of a layered condenser which includes a dielectric layer made from a ceramic such as titanium barium oxide or the like.
Furthermore, normally, for making this type of capacitor, and in particular for making its dielectric layer, a spattering method or a CVD method or a laser ablation method or the like is employed.
In this connection, the capacitance of a capacitor is proportional to the permittivity and to the area of its dielectric layer, and is inversely proportional to its thickness. Accordingly, if it is desired to produce a capacitor of small size and high capacitance for being fitted internally to a circuit, from the point of view of leak current, it is anticipated to increase its capacitance by making its dielectric layer from a material which has high permittivity. On the other hand, if it is desired to produce a capacitor which is to be fitted externally to a circuit, there is a strong demand to keep the cost of manufacture low and to enhance the yield rate, so that it is desirable to be able to manufacture the capacitor with a very thin dielectric layer in an easy manner.
Against this background, when the permittivity of the dielectric layer of a capacitor is considered in relation to the area and the layer thickness of the capacitor, it is considered desirable for this permittivity to be at least 300 in the case of a capacitor which is to be fitted internally to a circuit, and at least 1000 in the case of one which is to be fitted externally.
However, for a capacitor which is manufactured in the interior of a circuit, it is possible to utilize a layer of silicon oxide, a layer of silicon nitride, or a layer of oxidized silicon nitride or the like as the dielectric layer, these dielectric layers have a low permittivity which is less than or equal to 10, and accordingly, in order to enhance their capacitance, it is necessary to increase their area, or the like. If the area of the capacitor is increased in this manner, then the area which the capacitor occupies in the circuit becomes undesirably large, and this undesirably hinders the task of making the circuit more compact.
As materials which have high permittivity there are, for example, strongly dielectric materials such as titanium silicon oxide lead oxide and titanium barium oxide and the like. With this type of strongly dielectric material, it is necessary to keep the temperature at which their layer is manufactured to be below 450° C., due to the influence which is exerted upon other semiconductor elements and lead wires which are provided within the same semiconductor device. However, at this kind of low temperature, it is difficult for crystallization to take place, and accordingly the dielectric layer which is obtained is indeed one which has a high permittivity as compared with a silicon oxide layer or the like, but still it is not possible for it to attain the desired very high permittivity. In addition, the variation of the permittivity with respect to change of frequency and change of temperature is large, so that, from this point of view, the resulting component is one which is inferior, as compared to one which employs a silicon oxide layer or the like.
In addition, in a method of manufacture of this type of capacitor, and in particular since its dielectric layer is manufactured by utilizing a spattering method, a CVD method, a laser ablation method or the like, there are the problems that the initial cost which is required for purchase of a large scale layer manufacturing device becomes high, and furthermore the running cost also becomes high, since a large amount of energy is needed for manufacturing the layers. Moreover, if patterning is performed by etching after layer manufacture, the efficiency of utilization of the raw material is poor, and also the cost becomes undesirably high since various liquid chemicals come to be required for photo-litho masking and etching; furthermore, there is the problem that the productivity is deteriorated, since the number of processes is augmented.
On the other hand, in the case of manufacture of a capacitor which is intended to be fitted externally to a circuit, such as one which is made from a ceramic such as titanium barium oxide or the like, while the cost of the capacitor itself remains low, there are problems such as the fact that assembly cost is entailed by positioning the capacitor when fitting it externally and by bonding it or the like to other elements, and with regard to yield and so on, so that it is not possible to attain sufficient cost reduction.
The present invention has been conceived in the light of the above described problems, and it takes as its objective to provide: a capacitor which, due to incorporating a dielectric layer of high permittivity, is capable of promoting the compactness of a device in which it is incorporated; a method of manufacture of a capacitor which is capable of producing this capacitor at a low cost; and a semiconductor device which incorporates this type of capacitor.